In the production of gypsum products, especially in the production of gypsum moldings and construction materials obtainable therefrom, such as gypsum plasterboards, it is frequently necessary to improve water resistance. For this purpose, according to the prior art, the gypsum moldings are frequently rendered water-repellent. This can be done, for example, by applying a hydrophobic coating to a corresponding molding, for example by treatment with hydrophobing agents, or else by a so-called bulk hydrophobization, in which an appropriate hydrophobing agent is added to the gypsum constituents.
Hydrophobing additives for gypsum described in the prior art are a multitude of different materials.
For example, DE 100 49 072 A1 describes construction materials which comprise carboxylic ester-containing hydrophobing powders. According to the publication, the hydrophobing powder used is a redispersible dispersion powder which contains at least one carboxylic ester. A problem with the compositions described is that the hydrophobization is frequently not sufficiently effective and, furthermore, the carboxylic esters may be subjected to a hydrolysis process which alters the effect over time.
U.S. Pat. No. 6,547,874 B2 relates to a hydrophobing agent for gypsum-containing construction materials which comprise constituents treated with organopolysiloxanes. The use of siloxanes in the hydrophobization of gypsum-containing construction materials leads, however, in practice frequently to problems in the recycling of corresponding materials. Furthermore, setting a predefined or desired porosity is frequently made more difficult, since the silicones can act antagonistically to those compositions which are intended to impart porosity to the gypsum by inclusion of air. Furthermore, the use of corresponding silicones have the disadvantage that the materials are expensive and in some cases difficult to obtain.
DE 41 07 385 C2 relates to a dry pulverulent render mixture using calcined flue gas gypsum which contains assistants and additives. The use of fatty acid salts is not described.
DE 31 05 407 A1 relates to a water-repellent gypsum mortar which comprises, for hydrophobization, a fatty amine, a salt and an alkaline metal siliconate. The publication states that salts of fatty acids in the case of gypsum have only insufficient action with regard to hydrophobization.
DE 44 33 864 A1 relates to a process for water-repellent impregnation of gypsum by treatment with organosiloxanes and alkali metal silicate. The disadvantage which in the case of use of siloxanes or silicones has already been described above.
DE 32 42 598 A1 relates to a process for producing shaped bodies, more particularly bridges, using calcium sulfate-containing binders which comprise cellulose fibers, which have been impregnated with water in a particular manner. The use of fatty acid salts is not described in the publication.
DE 41 28 424 A1 describes a process for producing water-repellent porous gypsum moldings which comprise alkylhydropolysiloxanes.
DE 697 04 312 T2 relates to a gypsum mixture which comprises a hydrophobic additive. Here too, silanes are used for hydrophobization of the gypsum powder.
DE 195 06 398 A1 relates to a process for hydrophobizing gypsum materials, in which a water-redispersible dispersion powder based on vinyl acetate copolymers with ethylene and/or vinyl esters of C5-C15-monocarboxylic acids and the like is used for hydrophobization.
DE 196 28 749 A1 describes a process for hydrophobization of a more mineral carrier and hydrophobing agent for process performance, wherein the hydrophobing agent is used as specific montan wax fraction. Overall, it is found that the prior art principally addresses the use of silicones and waxes for hydrophobization of gypsum-containing construction materials. The use of fatty acid salts is not mentioned, or is described as disadvantageous and not appropriate to the aim. The methods and hydrophobing agents described in the context of the prior art, however, all have different fundamental problems. The compounds used are generally expensive, not always available, or not available in a sufficient amount, and are frequently produced on the basis of mineral oil. All these facts have clear disadvantages by virtue of a profile of properties for such compositions which is already becoming evident at present and is to be expected in the future. The hydrophobing of gypsum materials is expensive and unreliable, and meets the demands on a bulk product from an ecological point of view only in an inadequate manner, if at all.